Simple syntax In its simplest form, a PowerScript variable declaration requires only two parts:
the datatype and the variable name. For example:
datatype variablename
Full syntax The full syntax allows you to specify access and an initial value. Arrays and some datatypes, such as blobs and decimals, accept additional information:
{ access } datatype { { size } } { { precision } } variablename { = value } {, variablename2 { = value2 } }
Table 3-2: Variable declaration parameters Parameter Description
access (optional)
(For instance variables only) Keywords specifying the access for the variable. For information, see “Access for instance variables” on page 42.
datatype The datatype of the variable. You can specify a standard datatype, a system object, or a previously defined structure.
For blobs and decimals, you can specify the size or precision of the data by including an optional value in brackets.
{ size } (optional)
(For blobs only) A number, enclosed in braces, specifying the size in bytes of the blob. If { size } is omitted, the blob has an initial size of zero and PowerBuilder adjusts its size each time it is used at runtime.
If you enter a size that exceeds the declared length in a script, PowerBuilder truncates the blob data.
Declaring variables
Examples Declaring instance variables
integer ii_total = 100 // Total shares date id_date // Date shares were bought Declaring a global variable
string gs_name Declaring shared variables
time st_process_start string ss_process_name Declaring local variables
string ls_city = "Boston"
integer li_count
Declaring blobs This statement declares ib_Emp_Picture a blob with an initial length of zero. The length is adjusted when data is assigned to it:
blob ib_Emp_Picture
This statement declares ib_Emp_Picture a blob with a fixed length of 100 bytes:
blob{100} ib_Emp_Picture
Declaring decimals These statements declare shared variables sc_Amount and sc_dollars_accumulated as decimal numbers with two digits after the decimal point:
{ precision } (optional)
(For decimals only) A number, enclosed in braces, specifying the number of digits after the decimal point. If you do not specify a precision, the variable takes the precision assigned to it in the script.
variablename The name of the variable (must be a valid PowerScript identifier, as described in “Identifier names” on page 5).
You can define additional variables with the same datatype by naming additional variable names, separated by commas; each variable can have a value.
value (optional)
A literal or expression of the appropriate datatype that will be the initial value of the variable.
Blobs cannot be initialized with a value.
For information, see “Initial values for variables” on page 40.
Parameter Description
This statement declares lc_Rate1 and lc_Rate2 as decimal numbers with four digits after the decimal point:
dec{4} lc_Rate1, lc_Rate2
This statement declares lc_Balance as a decimal with zero digits after the decimal point:
decimal{0} lc_Balance
This statement does not specify the number of decimal places for lc_Result.
After the product of lc_Op1 and lc_Op2 is assigned to it, lc_Result has four decimal places:
dec lc_Result
dec{2} lc_Op1, lc_Op2 lc_Result = lc_Op1 * lc_Op2
Datatype of a variable
A PowerScript variable can be declared as one of the following datatypes:
• A standard datatype (such as an integer or string).
• An object or control (such as a window or CommandButton).
• An object or structure that you have defined (such as a window called mywindow). An object you have defined must be in a library on the application’s library search path when the script is compiled.
Variable names
In a well-planned application, standards determine how you name your PowerScript variables. Naming conventions make scripts easy to understand and help you avoid name conflicts. A typical approach is to include a prefix that identifies the scope and the datatype of the variable. For example, a prefix for an instance variable’s name typically begins with i (such as ii_count or is_empname), a local integer variable’s name would be li_total and a global integer variable’s name would be gi_total.
For information about naming conventions, see the PowerBuilder Users Guide.
Declaring variables
X and Y as variable
names Although you might think of x and y as typical variable names, in PowerBuilder they are also properties that specify an object’s onscreen coordinates. If you use them as variables and forget to declare them, you do not get a compiler error. Instead, PowerBuilder assumes you want to move the object, which might lead to unexpected results in your application.
Initial values for variables
When you declare a PowerScript variable, you can accept the default initial value or specify an initial value in the declaration.
Default values for
variables If you do not initialize a variable when you declare it, PowerBuilder sets the variable to the default value for its datatype as shown in the following table.
Table 3-3: Default initial values for variables
Specifying a literal as
a initial value To initialize a variable when you declare it, place an equal sign (=) and a literal appropriate for that variable datatype after the variable. For information about literals for specific datatypes, see “Standard datatypes” on page 21.
Do not use a function’s return value
You should not initialize a variable by assigning it the return value of a global user defined function, because it might not compile correctly, or because it could lead to confusion about the value assigned. For example, do not use:
integer i = f_return_one()
Although you can use global system functions or expressions to initialize variables with compile time values in a variable declaration statement, for runtime value assignments, you must also declare variables and assign their
For this variable datatype PowerBuilder sets this default value
Blob A blob of 0 length; an empty blob
Char (or character) ASCII value 0
Boolean false
Date 1900-01-01 (January 1, 1900)
DateTime 1900-01-01 00:00:00
Numeric (byte, integer, long, longlong, decimal, real, double, UnsignedInteger, and UnsignedLong)
0
String Empty string ("")
Time 00:00:00 (midnight)
This example declares li_count as an integer whose value is 5:
integer li_count=5
This example declares li_a and li_b as integers and initializes li_a to 5 and li_b to 10:
integer li_a=5, li_b=10
This example initializes ls_method with the string "UPS":
string ls_method="UPS"
This example initializes ls_headers to three words separated by tabs:
string ls_headers = "Name~tAddress~tCity"
This example initializes li_a to 1 and li_c to 100, leaving li_b set to its default value of zero:
integer li_a=1, li_b, li_c=100
This example declares ld_StartDate as a date and initializes it with the date February 1, 2004:
date ld_StartDate = 2004-02-01 Specifying an
expression as an initial value
You can initialize a variable with the value of an existing variable or expression, such as:
integer i = 100 integer j = i
When you do this, the second variable is initialized with the value of the expression when the script is compiled. The initialization is not reevaluated at runtime.
If the expression’s value changes Because the expression’s value is set to the variable when the script is compiled (not at runtime) make sure the expression is not one whose value is based on current conditions. If you want to specify an expression whose value will be different when the application is executed, do not initialize the variable in the declaration. For such values, declare the variable and assign the value in separate statements.
In this declaration, the value of d_date is the date the script is compiled:
date d_date = Today( )
In contrast, these statements result in d_date being set to the date the application is run:
date d_date
Declaring variables
How shared variables
are initialized When you use a shared variable in a script, the variable is initialized when the first instance of the object is opened. When the object is closed, the shared variable continues to exist until you exit the application. If you open the object again without exiting the application, the shared variable will have the value it had when you closed the object.
For example, if you set the shared variable Count to 20 in the script for a window, then close the window, and then reopen the window without exiting the application, Count will be equal to 20.
When using multiple instances of windows
If you have multiple instances of the window in the example above, Count will be equal to 20 in each instance. Since shared variables are shared among all instances of the window, changing Count in any instance of the window changes it for all instances.
How instance variables are initialized
When you define an instance variable for a window, menu, or application object, the instance variable is initialized when the object is opened. Its initial value is the default value for its datatype or the value specified in the variable declarations.
When you close the object, the instance variable ceases to exist. If you open the object again, the instance variable is initialized again.
When to use multiple instances of windows When you build a script for one of multiple instances of a window, instance variables can have a different value in each instance of the window. For example, to set a flag based on the contents of the instance of a window, you would use an instance variable.
When to use shared variables instead Use a shared variable instead of an instance variable if you need a variable that:
• Keeps the same value over multiple instances of an object
• Continues to exist after the object is closed
Access for instance variables
Description The general syntax for declaring PowerScript variables (see “Syntax of a variable declaration” on page 37) showed that you can specify access keywords in a declaration for an instance variable. This section describes those keywords.
When you specify an access right for a variable, you are controlling the visibility of the variable or its visibility access. Access determines which scripts recognize the variable’s name.
For a specified access right, you can control operational access with modifier keywords. The modifiers specify which scripts can read the variable’s value and which scripts can change it.
Syntax { access-right } { readaccess } { writeaccess } datatype variablename The following table describes the parameters you can use to specify access rights for instance variables.
Table 3-4: Instance variable declaration parameters for access rights Parameter Description
access-right (optional)
A keyword specifying where the variable’s name will be recognized. Values are:
• PUBLIC – (Default) Any script in the application can refer to the variable. In another object’s script, you use dot notation to qualify the variable name and identify the object it belongs to.
• PROTECTED – Scripts for the object for which the variable is declared and its descendants can refer to the variable.
• PRIVATE – Scripts for the object for which the variable is declared can refer to the variable. You cannot refer to the variable in descendants of the object.
readaccess (optional)
A keyword restricting the ability of scripts to read the variable’s value. Values are:
• PROTECTEDREAD – Only scripts for the object and its descendants can read the variable.
• PRIVATEREAD – Only scripts for the object can read the variable.
When access-right is PUBLIC, you can specify either keyword.
When access-right is PROTECTED, you can specify only PRIVATEREAD. You cannot specify a modifier for PRIVATE access, because PRIVATE is already fully restricted.
If readaccess is omitted, any script can read the variable.
Declaring variables
Usage Access modifiers give you more control over which objects have access to a particular object’s variables. A typical use is to declare a public variable but only allow the owner object to modify it:
public protectedwrite integer ii_count
You can also group declarations that have the same access by specifying the access-right keyword as a label (see "Another format for access-right keywords" next).
When you look at exported object syntax, you might see the access modifiers SYSTEMREAD and SYSTEMWRITE. Only PowerBuilder can access variables with these modifiers. You cannot refer to variables with these modifiers in your scripts and functions and you cannot use these modifiers in your own definitions.
Examples To declare these variables, select Declare>Instance Variables in the appropriate painter.
These declarations use access keywords to control the scripts that have access to the variables:
private integer ii_a, ii_n public integer ii_Subtotal protected integer ii_WinCount writeaccess
(optional)
A keyword restricting the ability of scripts to change the variable’s value. Values are:
• PROTECTEDWRITE – Only scripts for the object and its descendants can change the variable.
• PRIVATEWRITE – Only scripts for the object can change the variable.
When access-right is PUBLIC, you can specify either keyword.
When access-right is PROTECTED, you can specify only PRIVATEWRITE. You cannot specify a modifier for PRIVATE access, because PRIVATE is already fully restricted.
If writeaccess is omitted, any script can change the variable.
datatype A valid datatype. See “Syntax of a variable declaration” on page 37.
variablename A valid identifier. See “Syntax of a variable declaration” on page 37.
Parameter Description
This protected variable can only be changed by scripts of the owner object;
descendants of the owner can read it:
protected privatewrite string is_label
These declarations have public access (the default) but can only be changed by scripts in the object itself:
privatewrite real ir_accum, ir_current_data
This declaration defines an integer that only the owner objects can write or read but whose name is reserved at the public level:
public privateread privatewrite integer ii_reserved Private variable not recognized outside its object Suppose you have defined a window w_emp with a private integer variable ii_int:
private integer ii_int
In a script you declare an instance of the window called w_myemp. If you refer to the private variable ii_int, you get a compiler warning that the variable is not defined (because the variable is private and is not recognized in scripts outside the window itself):
w_emp w_myemp
w_myemp.ii_int = 1 // Variable not defined
Public variable with restricted access Suppose you have defined a window w_emp with a public integer variable ii_int with write access restricted to private:
public privatewrite integer ii_int
If you write the same script as above, the compiler warning will say that you cannot write to the variable (the name is recognized because it is public, but write access is not allowed):
w_emp w_myemp
w_myemp.ii_int = 1 // Cannot write to variable
Declaring variables
Another format for access-right keywords
Description You can also group declarations of PowerScript variables according to access by specifying the access-right keyword as a label. It appears on its own line, followed by a colon (:).
Syntax access-right:
{ readaccess } { writeaccess } datatype variablename
{ access-right } { readaccess } { writeaccess } datatype variablename { readaccess } { writeaccess } datatype variablename
Within a labeled group of declarations, you can override the access on a single line by specifying another access-right keyword with the declaration. The labeled access takes effect again on the following lines.
Examples In these declarations, the instance variables have the access specified by the label that precedes them. Another private variable is defined at the end, where private overrides the public label:
Private:
integer ii_a=10, ii_b=24 string is_Name, is_Address1 Protected:
integer ii_Units double idb_Results string is_Lname Public:
integer ii_Weight
string is_Location="Home"
private integer ii_test
Some of these protected declarations have restricted write access:
Protected:
integer ii_Units
privatewrite double idb_Results privatewrite string is_Lname